Golf ball resin composition and golf ball

ABSTRACT

An object of the present invention is to provide a golf ball resin composition with an excellent resilience and fluidity. Another object of the present invention is to provide a golf ball resin composition with a high hardness and durability. Yet another object of the present invention is to provide a golf ball traveling a great distance with an ionomer cover. The present invention provides a golf ball resin composition comprising, (A) an ionomer resin consisting of a metal ion-neutralized product of a binary copolymer composed of an olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; (B) a binary copolymer composed of an olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and (C) a zinc compound, wherein a content ratio ((A)/(B)) of (A) component to (B) component ranges from 50/50 to 80/20 in a mass ratio and a content of (C) component ranges from 0.1 part to 20 parts with respect to 100 parts by mass of a sum of (A) component and (B) component, and the golf ball resin composition has a melt flow rate (190° C., 2.16 kg) of 15 g/10 min or more.

FIELD OF THE INVENTION

The present invention relates to a golf ball resin composition and agolf ball, in particular, an improvement of a resilience and fluidity ofan ionomer resin composition.

DESCRIPTION OF THE RELATED ART

Ionomer resins and polyurethane are used as materials for constitutinggolf balls. Use of the ionomer resins as the constituting material ofthe golf ball provides the golf ball traveling a great distance, becauseof its high stiffness. Accordingly, ionomer resins are widely used as amaterial constituting a cover or an intermediate layer of the golf ball.However, there still remains a room for further improvement with respectto the stiffness and fluidity thereof and various improvements have beenproposed for improving these properties.

Japanese Patent Publication No. 2000-157646 A discloses a golf ballcover composition having a melt index (MI) of 1 dg/sec. or more andprimarily comprising a mixture of a base resin, blended with (d) a metalsoap obtained by neutralizing an organic acid having up to 29 carbonatoms with a monovalent to trivalent metal ion, in a mass ratio of thebase resin to the metal soap being 95:5 to 80:20, wherein the base resincomprises an ionomer resin component containing (a) a ternary ionomerresin consisting of a metal ion neutralized product of anolefin-unsaturated carboxylic acid-unsaturated carboxylate copolymerhaving an acid content of 12 wt % or less, and (b) a binary ionomerresin consisting of a metal ion neutralized product of anolefin-unsaturated carboxylic acid copolymer having an acid content of15 wt % or less in a ratio of 40:60 to 100:0; and (c) an unneutralizedrandom copolymer composed of olefin and unsaturated carboxylic acidmonomers, in a mass ratio of the ionomer resin component to (c) theunneutralized random copolymer being 75:25 to 100:0.

U.S. Pat. No. 5,306,760 discloses a golf ball comprising a core and acover, wherein the cover consists essentially of 100 parts by weight ofat least one ionomer resin and from about 25 to about 100 parts byweight of fatty acid salt, wherein said ionomer resin is the reactionproduct of an olefin having from 2 to 8 carbon atoms and an unsaturatedmonocarboxylic acid having from 3 to 8 carbon atoms.

U.S. Pat. No. 5,312,857 discloses a golf ball comprising a core and acover, wherein the cover consists essentially of 100 parts by weight ofat least one ionomer resin and from about 25 to about 100 parts byweight of a metal stearate, wherein said ionomer resin is the reactionproduct of an olefin having from 2 to 8 carbon atoms and an unsaturatedmonocarboxylic acid having from 3 to 8 carbon atoms.

Japanese Patent Publication No. H06-292740 A discloses a composition fora golf ball cover material which comprises (A) 15 to 90 parts by weightof metal salts of an ethylene/ethylenically unsaturated monocarboxylicacid copolymer having an ethylenically unsaturated monocarboxylic acidcontent of 10 to 30% by weight and a degree of neutralization of atleast of 25 mole % and (B) 85 to 10 parts by weight of anethylene/(meth)acrylate ester/ethylenically unsaturated monocarboxylicacid terpolymer having a (meth)acrylate ester content of 12 to 45% byweight and an ethylenically unsaturated monocarboxylic acid content of0.5 to 5% by weight.

Japanese Patent Publication No. 2001-218873 A discloses a multi-piecegolf ball comprising a solid core, an intermediate layer enclosing thesolid core, and a cover enclosing the intermediate layer, wherein atleast one of said intermediate layer and said cover is formed of aheated mixture comprising (a) 100 parts by weight of anolefin-unsaturated carboxylic acid random copolymer or anolefin-unsaturated carboxylic acid-unsaturated carboxylate randomcopolymer or both of them, (b) 5 to 80 parts by weight of a fatty acidhaving a molecular weight of at least 280 or a derivative thereof, and(c) 0.1 to 10 parts by weight of a basic inorganic metal compoundcapable of neutralizing acid groups in components (a) and (b), saidheated mixture having a melt index of at least 1.0 dg/min, and whereinsaid intermediate layer has a Shore D hardness of 40 to 63, said coverhas a Shore D hardness of 45 to 68, and the Shore D hardness of saidsolid core at its center is not greater than the Shore D hardness ofsaid intermediate layer, which is not greater than the Shore D hardnessof said cover.

Japanese Patent Publication No. 2002-219195 A discloses a golf ballmaterial comprising a mixture which is composed of essential components:100 parts by weight of a resinous component consisting of a base resinand (e) a non-ionomer thermoplastic elastomer, the base resin and theelastomer being blended in a weight ratio of 100:0 to 50:50; (c) 5 to 80parts by weight of a fatty acid and/or fatty acid derivative having amolecular weight of 280 to 1,500; and (d) 0.1 to 10 parts by weight of abasic inorganic metal compound capable of neutralizing acidic groupsleft unneutralized in the base resin and component (c), wherein the baseresin has (a) an olefin-unsaturated carboxylic acid binary randomcopolymer and/or a metal ion-neutralized olefin-unsaturated carboxylicacid binary random copolymer, blended with (b) an olefin-unsaturatedcarboxylic acid-unsaturated carboxylate ternary random copolymer and/ora metal ion neutralized olefin-unsaturated carboxylic acid-unsaturatedcarboxylate ternary random copolymer, in a weight ratio of 100:0 to25:75.

SUMMARY OF THE INVENTION

The improvement in a flight distance of a golf ball using an ionomerresin has been addressed. An approach to improve a flight distance is toenlarge a diameter of a core part having a high resilience. In order toenlarge a diameter of the core, it is necessary to mold a thinnerionomer cover. However, it is difficult to mold a thin ionomer cover byan injection molding method. In addition, the thin ionomer cover oftencauses a lower durability. Another approach to improve a flight distanceis to use an ionomer resin having a high degree of neutralization.However, since the ionomer resin having a high degree of neutralizationhas low fluidity, it is extremely difficult to injection mold a thincover. As a method of improving the fluidity of the ionomer resin, it isknown that a low molecular weight material such as a fatty acid or ametal salt thereof is added to the ionomer resin having a high degree ofneutralization. However, since a considerable amount of the lowmolecular weight material must be added in order to improve thefluidity, the low molecular weight material tends to bleed out from thesurface of the golf ball body, which causes a problem of lower adhesionof the paint film when applying a paint to the surface of the golf ballbody. Another method of improving the fluidity of the ionomer resin, itis known that an ethylene-(meth)acrylic acid binary copolymer or anethylene-(meth)acrylic acid-(meth)acrylic acid ester ternary copolymeris added to the ionomer resin. However, the hardness of the resultantblend becomes low, which causes a shorter flight distance because of anincreased spin rate on driver shots.

As described above, in order to improve a flight distance of the golfball using an ionomer resin as a cover material, it is necessary to usea cover material having a high resilience, mold a thin cover, andincrease a cover hardness. However, since the ionomer resin having ahigh degree of neutralization has a low fluidity, it is difficult tomold a thin cover. Further, the cover having a high hardness causes aproblem of lower durability.

The present invention has been achieved in view of the abovecircumstances. An object of the present invention is to provide a golfball resin composition with an excellent resilience and fluidity.Another object of the present invention is to provide a golf ball resincomposition with a high hardness and durability. Yet another object ofthe present invention is to provide a golf ball traveling a greatdistance with an ionomer cover.

The present invention provides a golf ball resin composition comprising,(A) an ionomer resin consisting of a metal ion-neutralized product of abinary copolymer composed of an olefin and an α,β-unsaturated carboxylicacid having 3 to 8 carbon atoms; (B) a binary copolymer composed of anolefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbonatoms, and (C) a zinc compound, wherein a content ratio ((A)/(B)) of (A)component to (B) component ranges from 50/50 to 80/20 in a mass ratioand a content of (C) component ranges from 0.1 part to 20 parts withrespect to 100 parts by mass of a sum of (A) component and (B)component, and the golf ball resin composition has a melt flow rate(190° C., 2.16 kg) of 15 g/10 min or more.

(A) The binary ionomer resin mainly contained in the golf ball resincomposition of the present invention improves the resilience of theresultant golf ball. Further, (B) the binary copolymer composed of anolefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atomsimproves the fluidity of the golf ball resin composition. Further, thegolf ball resin composition of the present invention features (C) a zinccompound. (C) The zinc compound is used to neutralize non-neutralizedcarboxyl groups existing in (A) component and (B) component, therebyimproving a resilience of the resin composition. Since (C) the zinccompound with a relatively slow neutralization rate is used, theneutralization does not proceed so much in a melt-mixing step or anextruding step of the golf ball resin composition. Thus, the golf ballresin composition maintains a good fluidity. Since the neutralizationproceed in a step of molding in a mold, the resultant golf ball resincomposition has as high resilience as the ionomer resin having a highneutralization degree. Consequently, the golf ball resin composition ofthe present invention enables to strike a balance between the fluidityand resilience. Further, according to the present invention, use of (C)the zinc compound for neutralizing non-neutralized carboxyl groupsexisting in (A) component and (B) component provides a golf ball havinga good durability, irrespective of the cover having a high hardness. Yetfurther, since the golf ball resin composition of the present inventiondoes not contain a low molecular material such as a fatty acid or ametal salt thereof which bleeds out from the surface of the golf ballbody, the adhesion of the paint film is excellent.

The present invention includes the golf ball resin composition beforecarboxyl groups existing in (A) component and (B) component areneutralized with (C) the zinc compound, and the golf ball resincomposition after the neutralization proceeded. It is noted that thegolf ball resin composition after the neutralization proceeded includesthe composition after the neutralization proceeded partially. In thepresent invention, the golf ball resin composition before neutralizationmay be referred to as “non-neutralized golf ball resin composition,” andthe golf ball resin composition after neutralization may be referred toas “neutralized golf ball resin composition,” respectively. Simplyreferred “golf ball resin composition” includes both embodiments, unlessotherwise described.

The present invention further provides a golf ball having a constituentmember formed by injection molding the golf ball resin composition ofthe present invention. The constituent member preferably includes acover. In this case, the cover preferably has a thickness ranging from0.5 mm to 1.5 mm.

According to the present invention, the golf ball resin composition withan excellent resilience and fluidity is obtained. Further, the golf ballresin composition of the present invention has a high hardness anddurability. According to the present invention, the golf ball travelinga great distance with an ionomer cover is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a FT-IR spectrum of one embodiment of the golf ball resincomposition of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a golf ball resin composition comprising,(A) an ionomer resin consisting of a metal ion-neutralized product of abinary copolymer composed of an olefin and an α,β-unsaturated carboxylicacid having 3 to 8 carbon atoms; (B) a binary copolymer composed of anolefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbonatoms, and (C) a zinc compound, wherein a content ratio ((A)/(B)) of (A)component to (B) component ranges from 50/50 to 80/20 in a mass ratioand a content of (C) component ranges from 0.1 part to 20 parts withrespect to 100 parts by mass of a sum of (A) component and (B)component, and the golf ball resin component has a melt flow rate (190°C., 2.16 kg) of 15 g/10 min or more.

First, (A) the ionomer resin consisting of a metal ion-neutralizedproduct of a binary copolymer composed of an olefin and anα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms (hereinafter,sometimes merely referred to as “binary ionomer resin”) will beexplained. (A) The ionomer resin includes, for example, one prepared byneutralizing at least a part of carboxyl groups in a binary copolymercomposed of an olefin and an α,β-unsaturated carboxylic acid having 3 to8 carbon atoms with a metal ion. The olefin preferably includes anolefin having 2 to 8 carbon atoms. Examples of the olefin are ethylene,propylene, butene, pentene, hexene, heptene, and octene. The olefin morepreferably includes ethylene. Examples of the α,β-unsaturated carboxylicacid having 3 to 8 carbon atoms are acrylic acid, methacrylic acid,fumaric acid, maleic acid and crotonic acid. Among these, acrylic acidand methacrylic acid are particularly preferred. As (A) the binaryionomer resin, preferred is the metal ion-neutralized product of thebinary copolymer composed of ethylene-(meth)acrylic acid. Herein,“(meth)acrylic acid” means acrylic acid and/or methacrylic acid.

The content of the α,β-unsaturated carboxylic acid having 3 to 8 carbonatoms in (A) the binary ionomer resin is preferably 15 mass % or more,more preferably 16 mass % or more, even more preferably 17 mass % ormore, and is preferably 30 mass % or less, more preferably 25 mass % orless. If the content of the α,β-unsaturated carboxylic acid having 3 to8 carbon atoms is 15 mass % or more, the resultant constituent memberhas a desirable hardness. If the content of the α,β-unsaturatedcarboxylic acid having 3 to 8 carbon atoms is 30 mass % or less, sincethe hardness of the resultant constituent member does not becomeexcessively high, the durability and shot feeling become better.

The degree of neutralization of the carboxyl groups contained in thebinary ionomer resin is preferably 15 mole % or more, more preferably 20mole % or more, and is preferably 90 mole % or less, more preferably 85mole % or less. If the degree of neutralization is 15 mole % or more,the resultant golf ball has better resilience and durability. If thedegree of neutralization is 90 mole % or less, the golf ball resincomposition has better fluidity (good moldability). The degree ofneutralization of the carboxyl groups in the binary ionomer resin can becalculated by the following expression.Degree of neutralization (mol %) of the binary ionomer resin=(the numberof moles of carboxyl groups neutralized in the binary ionomer resin/thenumber of moles of all carboxyl groups contained in the binary ionomerresin)×100

Examples of a metal (ion) used for neutralizing at least a part ofcarboxyl groups of the binary ionomer resin include: monovalent metalsions such as sodium, potassium, lithium, or the like; divalent metalsions such as magnesium, calcium, zinc, barium, cadmium, or the like;trivalent metals ions such as aluminum or the like; and other metals(ions) such as tin, zirconium, or the like. (A) The binary ionomer resinused in the present invention is preferably neutralized with zinc. Useof (A) the binary ionomer resin neutralized with zinc provides a golfball with a good durability and low temperature durability.

Specific examples of the binary ionomer resin include trade name“Himilan (registered trademark) (e.g. Himilan 1555 (Na), Himilan 1557(Zn), Himilan 1605 (Na), Himilan 1706 (Zn), Himilan 1707 (Na), HimilanAM7311 (Mg), Himilan AM7329 (Zn))” commercially available from DuPont-Mitsui Polychemicals Co., Ltd.

Further, examples include “Surlyn (registered trademark) (e.g. Surlyn8945 (Na), Surlyn 9945 (Zn), Surlyn 8140 (Na), Surlyn 8150 (Na), Surlyn9120 (Zn), Surlyn 9150 (Zn), Surlyn 6910 (Mg), Surlyn 6120 (Mg), Surlyn7930 (Li), Surlyn 7940 (Li), Surlyn AD8546 (Li))” commercially availablefrom E.I. du Pont de Nemours and Company.

Further, examples include “Iotek (registered trademark) (e.g. Iotek 8000(Na), Iotek 8030 (Na), Iotek 7010 (Zn), Iotek 7030 (Zn))” commerciallyavailable from ExxonMobil Chemical Corporation.

The binary ionomer resins may be used alone or as a mixture of at leasttwo of them. It is noted that Na, Zn, Li, and Mg described in theparentheses after the trade names indicate metal types of neutralizingmetal ions of the binary ionomer resins.

(A) The binary ionomer resin preferably has a bending stiffness of 140MPa or more, more preferably 150 MPa or more, even more preferably 160MPa or more, and preferably has a bending stiffness of 550 MPa or less,more preferably 500 MPa or less, even more preferably 450 MPa or less.If the bending stiffness of (A) the binary ionomer resin is too low, theflight distance tends to be shorter because of the increased spin rateon driver shots. If the bending stiffness is too high, the durability ofthe golf ball may be lowered.

The melt flow rate (190° C., 2.16 kg) of (A) the binary ionomer resin ispreferably 0.1 g/10 min or more, more preferably 0.5 g/10 min or more,and even more preferably 1.0 g/10 min or more, and is preferably 30 g/10min or less, more preferably 20 g/10 min or less, even more preferably15 g/10 min or less. If the melt flow rate of (A) the binary ionomerresin is 0.1 g/10 min or more, the golf ball resin composition hasbetter fluidity, and for example, it is easy to mold the thin-walledcover. If the melt flow rate of (A) the binary ionomer resin is 30 g/10min or less, the durability of the resultant golf ball becomes better.

(A) The binary ionomer resin preferably has a slab hardness of 50 ormore, more preferably 55 or more, even more preferably 60 or more, andpreferably has a slab hardness of 75 or less, more preferably 73 orless, even more preferably 70 or less in Shore D hardness. If the binaryionomer resin has a slab hardness of 50 or more in Shore D hardness, theresultant constituent member has a high hardness. If the binary ionomerresin has a slab hardness of 75 or less in Shore D hardness, theresultant constituent member does not become excessively hard and thusthe obtained golf ball has better durability.

Next, (B) the binary copolymer composed of an olefin and anα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms (hereinafter,sometimes merely referred to as “binary copolymer”) will be explained.The binary copolymer enhances the fluidity of the golf ball resincomposition.

(B) The binary copolymer is a nonionic copolymer of an olefin and anα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms wherein thecarboxyl groups thereof are not neutralized. Examples of the olefin andthe α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms includethe same olefin and α,β-unsaturated carboxylic acid having 3 to 8 carbonatoms exemplified as constituents of “(A) the binary ionomer resin.” (B)The binary copolymer preferably includes a binary copolymer composed ofethylene and (meth)acrylic acid.

The melt flow rate (190° C., 2.16 kg) of (B) the binary copolymer ispreferably 100 g/10 min or more, more preferably 150 g/10 min or more,and even more preferably 200 g/10 min or more, and is preferably 1,500g/10 min or less, more preferably 1,000 g/10 min or less even morepreferably 800 g/10 min or less. If the melt flow rate (190° C., 2.16kg) of (B) the binary copolymer is 100 g/10 min or more, the golf ballresin composition has better fluidity, and thus it is easy to mold athin cover. If the melt flow rate (190° C., 2.16 kg) of (B) the binarycopolymer is 1,500 g/10 min or less, the resultant golf ball has betterdurability.

Specific examples of (B) the binary copolymer include anethylene-methacrylic acid copolymer such as “NUCREL (registeredtrademark) (e.g. NUCREL N1050H, NUCREL N2050H, NUCREL AN4318, NUCRELN1110H, NUCREL N0200H) manufactured by Du Pont-Mitsui Polychemicals Co,and an ethylene-acrylic acid copolymer such as “PRIMACORE (registeredtrademark) 59801” available from Dow Chemical Company.

Next, (C) the zinc compound will be explained. (C) The zinc compound isused to neutralize non-neutralized carboxyl groups existing in (A)component and (B) component, thereby improving the resilience of theresin composition. Since (C) the zinc compound with a relatively slowneutralization rate is used, the neutralization does not proceed so muchin a melt-mixing step or an extruding step of the golf ball resincomposition. Thus, the golf ball resin composition maintains a goodfluidity. Since the neutralization proceed in a step of molding in amold, the resultant golf ball resin composition has as high a resilienceas the ionomer resin having a high neutralization degree. Examples of(C) the zinc compounds are an oxide (zinc oxide), a hydroxide (zinchydroxide), a sulfide (zinc sulfide), a phosphide, a halide (zincfluoride, zinc chloride, zinc bromide, zinc iodide), a salt of anoxoacid (zinc sulfate, zinc carbonate, zinc phosphate), an organic zinccompound (dimethylzinc, diphenylzinc, etc), and a complex compound, inaddition to a zinc powder. Among them, as (C) the zinc compound,preferred is zinc oxide (ZnO), zinc hydroxide (Zn(OH)₂), or zinccarbonate (ZnCO₃). Since these zinc compound have an appropriateneutralizing ability, it is possible to strike a balance between thefluidity and resilience. (C) The zinc compound, without limitation,preferably has shapes such as a granular form, plate-like form,needle-like form, and a tetra pod form (for example, “Pana-tetra”available from AMTEC. Co., Ltd.). It is noted that the zinc oxide isused as a pigment or a specific gravity adjusting agent for the cover,but the surface of the zinc oxide for use in the pigment or the specificgravity adjusting agent is often treated in order to improve thedispersibility to the cover material. On the other hand, the zinc oxideused in the present invention is preferably not surface-treated orslightly surface-treated in order to enhance the neutralization ability.

If the golf ball resin composition before injection molding is analyzedwith FT-IR (Fourier transform infrared spectrophotometer), A1 is definedas an area under a peak around 1600 cm⁻¹ and B1 is defined as an areaunder a peak around 1700 cm⁻¹ in the obtained spectrum and P1 is definedby the following equation; P1=A1/(A1+B1). P1 is preferably 0.20 or more,more preferably 0.21 or more, even more preferably 0.25 or more, and ispreferably 1.0 or less, more preferably 0.99 or less, even morepreferably 0.5 or less. If P1 falls within the above range, the golfball resin composition has a good fluidity at the injection molding. Inthe equation, A1 corresponds to an area under the peak attributed to theneutralized carboxyl group, and B1 corresponds to an area under the peakattributed to the non-neutralized carboxyl group. P1 is defined as aratio of the neutralized carboxyl groups to the whole carboxyl groupsand indicates a degree of neutralization of the golf ball resincomposition.

If the golf ball resin composition after injection molding is analyzedwith FT-IR (Fourier transform infrared spectrophotometer), A2 is definedas an area under a peak around 1600 cm⁻¹ and B2 is defined as an areaunder a peak around 1700 cm⁻¹ in the obtained spectrum and P2 is definedby the following equation; P2=A2/(A2+B2). P2 is preferably 0.3 or more,more preferably 0.31 or more, and is preferably 1.0 or less, morepreferably 0.99 or less. If P2 falls within the above range, the golfball resin composition has a good resilience. In the equation, A2corresponds to an area under the peak attributed to the neutralizedcarboxyl group, and B2 corresponds to an area under the peak attributedto the non-neutralized carboxyl group. P2 is defined as a ratio of theneutralized carboxyl groups to the whole carboxyl groups and indicates adegree of neutralization of the golf ball resin composition.

P2/P1 is preferably 1.5 or more, more preferably 1.6 or more, even morepreferably 1.7 or more and is preferably 2.5 or less, more preferably2.4 or less, even more preferably 2.3 or less. P2/P1 indicates a changein the degree of the neutralization of the golf ball before and afterthe injection molding. If P2/P1 is equal to or more than the lowerlimit, the effect of improving the resilience by the neutralization withthe zinc compound becomes large, while if P2/P1 is equal to or less thanthe upper limit, the neutralization does not proceed excessively. Thus,the golf ball resin composition maintains the fluidity and the injectionmolding becomes easy.

In the golf ball resin composition, a content ratio (A)/(B) of (A) thebinary ionomer resin to (B) the binary copolymer preferably ranges from50/50 to 80/20, more preferably from 55/45 to 75/25, even morepreferably 60/40 to 70/30 in a mass ratio. If the content ratio (A)/(B)of (A) component to (B) component falls within the above range, itbecomes easy to strike a balance between the high hardness and highfluidity.

The content of (C) the zinc compound contained in the golf ball resincomposition of the present invention is preferably 0.1 part by mass ormore, more preferably 0.2 part by mass or more, even more preferably 0.5part by mass or more, and is preferably 20 parts by mass or less, morepreferably 15 parts by mass or less, even more preferably 10 parts bymass or less with respect to 100 parts by mass of a sum of (A) componentand (B) component. If the content of (C) the zinc compound is 0.1 partby mass or more with respect to 100 parts by mass of a sum of (A)component and (B) component, the durability of the obtained golf ballimproves. On the other hand, if the content of (C) the zinc compound is20 parts by mass or less with respect to 100 parts by mass of a sum of(A) component and (B) component, the golf ball resin composition canmaintain the fluidity.

In the present invention, the golf ball resin composition may furthercontain a pigment component such as a white pigment (for example,titanium oxide), a blue pigment or the like; a specific gravityadjusting agent; a dispersant; an antioxidant; an ultraviolet absorber;a light stabilizer; a fluorescent material; a fluorescent brightener; orthe like, as long as they do not impair the effect of the presentinvention. In the golf ball resin composition, a fatty acid or a metalsalt thereof may be used in combination as a fluidity improving agent tothe extent that the effect of the present invention does notdeteriorate. However, it is not preferable that the low molecularmaterials such as the fatty acid or the metal salt thereof are used incombination, because the low molecular materials causes low adhesion ofthe paint film and low mechanical properties.

The amount of the white pigment (for example, titanium oxide), withrespect to 100 parts by mass of the resin component, is preferably 0.5part by mass or more, more preferably 1 part by mass or more, and ispreferably 10 parts by mass or less, more preferably 8 parts by mass orless. If the amount of the white pigment is 0.5 parts by mass or more,it is possible to impart the opacity to the constituent member of thegolf ball. If the amount of the white pigment is more than 10 parts bymass, the durability of the constituent member of the golf ball maydeteriorate.

The golf ball resin composition of the present invention preferablyconsists of (A) the binary ionomer resin and (B) the binary copolymer asa resin component, but may further contain another thermoplasticelastomer or another thermoplastic resin to the extent that the effectof the present invention does not deteriorate. In this case, the totalcontent of (A) the binary ionomer resin and (B) the binary copolymer inthe resin component of the golf ball resin composition is preferably 50mass % or more, more preferably 70 mass % or more, even more preferably90 mass % or more.

Examples of other thermoplastic elastomers are a thermoplastic polyamideelastomer having a commercial name of “Pebax (registered trademark)(e.g. “Pebax 2533”)” commercially available from Arkema K. K.; apolyurethane elastomer having a commercial name of “Elastollan(registered trademark) (e.g. “Elastollan XNY85A”)” commerciallyavailable from BASF Japan Ltd; a thermoplastic polyester elastomerhaving a commercial name of “Hytrel (registered trademark) (e.g. “Hytrel3548”, “Hytrel 4047”)” commercially available from Du Pont-Toray Co.,Ltd.; a thermoplastic polystyrene elastomer having a commercial name of“Rabalon (registered trademark) (e.g. “Rabalon T3221C”)” commerciallyavailable from Mitsubishi Chemical Corporation. Examples of thethermoplastic resin include an ionomer resin of the ternary copolymercomposed of an olefin, α,β-unsaturated carboxylic acid having 3 to 8carbon atoms, and α,β-unsaturated carboxylic acid ester.

The golf ball resin composition of the present invention can beobtained, for example, by dry blending (A) the binary ionomer resin, (B)the binary copolymer, and (C) the zinc compound. The dry blended mixturemay be extruded in the form of pellet. The dry blending may be carriedout using for example, a mixer capable of blending a raw material in theform of pellet, more preferably a tumbler type mixer. Extruding can becarried out by publicly known extruders such as a single-screw kneadingextruder, a twin-screw kneading extruder, and a twin-single kneadingextruder. The extruding condition is not particularly limited. Forexample, in the case of extruding with a twin-screw kneading extruder,the preferable conditions are screw diameter=45 mm; screw revolutions=50rpm to 400 rpm; screw L/D=35, and cylinder temperature; 140° C. to 200°C. If the extruding temperature exceeds 200° C., the neutralizationproceeds and the fluidity may be lowered.

The melt flow rate (190° C., 2.16 kg) of the golf ball resin compositionof the present invention is preferably 15 g/10 min or more, morepreferably 16 g/10 min or more, and even more preferably 18 g/10 min ormore, and is preferably 100 g/10 min or less, more preferably 70 g/10min or less, even more preferably 40 g/10 min or less. If the melt flowrate of the golf ball resin composition falls within the above range,the moldability becomes better.

The golf ball resin composition of the present invention preferably hasa slab hardness of 55 or more, more preferably 57 or more, even morepreferably 60 or more, and preferably has a slab hardness of 75 or less,more preferably 73 or less, even more preferably 70 or less in Shore Dhardness. Use of the golf ball resin composition having a slab hardnessof 55 or more in Shore D hardness reduces the spin rate of the resultantgolf ball on driver shots. Thus, the golf ball traveling a greatdistance is obtained. On the other hand, use of the golf ball resincomposition having a slab hardness of 75 or less in Shore D hardnessprovides a golf ball with excellent durability. Herein, the slabhardness of the golf ball resin composition is a measured hardness ofthe golf ball resin composition that is molded into a sheet form by ameasuring method described later.

The golf ball of the present invention is not limited, as long as itcomprises a constituent member formed from the golf ball resincomposition of the present invention. For example, in a two-piece golfball comprising a single-layered core and a cover disposed around thecore, in a three-piece golf ball comprising a core having a center and asingle-layered intermediate layer disposed around the center, and acover disposed around the core, and in a multi-piece golf ballcomprising a core having a center and at least one intermediate layerdisposed around the center, and a cover disposed around the core(including the three-piece golf ball mentioned above), anyone ofconstituent members is formed from the above golf ball resincomposition. In one preferable embodiment, the golf ball has the coverthat is injection molded from the golf ball resin composition of thepresent invention. In the followings, the present invention will beexplained based on the preferable embodiment where the golf ball resincomposition of the present invention is used as the cover composition.However, the present invention is not limited to this embodiment.

The cover of the golf ball of the present invention is formed from acover composition. An embodiment for molding a cover is not particularlylimited, and includes an embodiment which comprises injection moldingthe cover composition directly onto the core, or an embodiment whichcomprises molding the cover composition into a hollow-shell, coveringthe core with a plurality of the hollow-shells and subjecting the corewith a plurality of the hollow shells to the compression-molding(preferably an embodiment which comprises molding the cover compositioninto a half hollow-shell, covering the core with the two halfhollow-shells, and subjecting the core with the two half hollow-shellsto the compression-molding). The cover of the golf ball of the presentinvention is preferably formed by injection molding. The cover can beproduced more easily by injection molding.

In the case of directly injection molding the cover composition onto thecore, it is preferred to use upper and lower molds for forming a coverhaving a spherical cavity and pimples, wherein a part of the pimple alsoserves as a retractable hold pin. When forming the cover by injectionmolding, the hold pin is protruded to hold the core, and the covercomposition which has been heated and melted is charged and then cooledto obtain a cover.

In the case of molding the cover using the injection molding apparatusprovided with an injection unit and a mold unit, a temperature (settingtemperature of the injection unit) at the cylinder (barrel) portion ofthe injection unit is preferably 200° C. or more, more preferably 210°C. or more, and is preferably 270° C. or less, more preferably 260° C.or less. If the temperature of the cylinder (barrel) portion fallswithin the above range, the golf ball resin composition can maintain thefluidity and the neutralization of non-neutralized carboxyl groupsexisting in (A) component and (B) component with (C) the zinc compoundproceeds.

When molding a cover, the concave portions called “dimple” are usuallyformed on the surface. After the cover is molded, the mold is opened andthe golf ball body is taken out from the mold, and as necessary, thegolf ball body is preferably subjected to surface treatments such asdeburring, cleaning, and sandblast. If desired, a paint film or a markmay be formed. The paint film preferably has a thickness of, but notlimited to, 5 μm or larger, and more preferably 7 μm or larger, andpreferably has a thickness of 25 μm or smaller, and more preferably 18μm or smaller. If the thickness is smaller than 5 μm, the paint film iseasy to wear off due to continued use of the golf ball, and if thethickness is larger than 25 μm, the effect of the dimples is reduced,resulting in deteriorating flying performance of the golf ball.

In the present invention, the thickness of the cover of the golf ball ispreferably 1.5 mm or less, more preferably 1.3 mm or less, even morepreferably 1.0 mm or less. If the thickness of the cover is 1.5 mm orless, the resilience can be enhanced by enlarging a diameter of thecore. The thickness of the cover is preferably 0.5 mm or more, morepreferably 0.6 mm or more, and even more preferably 0.7 mm or more. Ifthe thickness of the cover is less than 0.5 mm, it may become difficultto mold the cover.

The cover preferably has a slab hardness of 55 or more, more preferably57 or more, even more preferably 60 or more, and preferably has a slabhardness of 75 or less, more preferably 73 or less, even more preferably70 or less in Shore D hardness. If the slab hardness of the cover isless than 55 in Shore D hardness, the spin rate on driver shotsincrease. Thus, the flight distance becomes shorter. On the other hand,if the slab hardness of the cover is more than 75 in Shore D hardness,the durability of the resultant golf ball may be lowered. Herein, theslab hardness of the cover is a measured hardness of the covercomposition that is molded into a sheet form by a measuring methoddescribed later.

Next, the core used for the golf ball of the present invention will beexplained. The construction of the core includes a single-layered core,and a core having a center and at least one intermediate layer coveringthe center. The core having a center and at least one intermediate layercovering the center includes a core consisting of a center and asingle-layered intermediate layer covering the center and a coreconsisting of a center and multi-piece of or multi-layer of theintermediate layers covering the center. The core preferably has aspherical shape. If the core does not have a spherical shape, the coverdoes not have a uniform thickness. As a result, there exist someportions where the performance of the cover is lowered. On the otherhand, the center generally has the spherical shape, but the center maybe provided with a rib on the surface thereof so that the surface of thespherical center is divided by the ribs. For example, the surface of thespherical center is evenly divided by the ribs. In one embodiment, theribs are preferably formed on the surface of the spherical center in anintegrated manner, and in another embodiment, the ribs are formed as anintermediate layer on the surface of the spherical center.

The ribs are preferably formed along an equatorial line and meridiansthat evenly divide the surface of the spherical center, if the sphericalcenter is assumed as the earth. For example, if the surface of thespherical center is evenly divided into 8, the ribs are formed along theequatorial line, any meridian as a standard, and meridians at thelongitude 90 degrees east, longitude 90 degrees west, and the longitude180 degrees east(west), assuming that the meridian as the standard is atlongitude 0 degree. If the ribs are formed, the depressed portiondivided by the ribs are preferably filled with a plurality ofintermediate layers or with a single-layered intermediate layer thatfills each of the depressed portions to make a core in the sphericalshape. The shape of the ribs, without limitation, includes an arc or analmost arc (for example, a part of the arc is removed to obtain a flatsurface at the cross or orthogonal portions thereof).

The center or core of the golf ball of the present invention can bemolded by, for example, heat-pressing a rubber composition (hereinafter,sometimes simply referred to as “core rubber composition”) containing abase rubber, a crosslinking initiator, a co-crosslinking agent, and afiller.

As the base rubber, a natural rubber and/or a synthetic rubber may beused. Examples of the base rubber are a polybutadiene rubber, a naturalrubber, a polyisoprene rubber, a styrene polybutadiene rubber, and anethylene-propylene-diene terpolymer (EPDM). Among them, typicallypreferred is the high cis-polybutadiene having cis-1,4-bond in aproportion of 40% or more, more preferably 70% or more, even morepreferably 90% or more in view of its superior resilience property.

The crosslinking initiator is blended to crosslink the base rubbercomponent. As the crosslinking initiator, an organic peroxide ispreferably used. Examples of the organic peroxide for use in the presentinvention are dicumyl peroxide,1,1-bis(t-butylperoxy)-3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Amongthem, dicumyl peroxide is preferable. An amount of the crosslinkinginitiator to be blended in the rubber composition is preferably 0.2 partby mass or more, more preferably 0.3 part by mass or more, and ispreferably 3 parts by mass or less, more preferably 2 parts by mass orless based on 100 parts by mass of the base rubber. If the amount isless than 0.2 part by mass, the core becomes too soft, and theresilience tends to be lowered, and if the amount is more than 3 partsby mass, the amount of the co-crosslinking agent must be increased inorder to obtain the appropriate hardness, which tends to cause theinsufficient resilience.

The co-crosslinking agent is not particularly limited as long as itserves to crosslink a rubber molecule by graft polymerization to a baserubber molecular chain; for example, α,β-unsaturated carboxylic acidhaving 3 to 8 carbon atoms or a metal salt thereof, more preferablyacrylic acid, methacrylic acid or a metal salt thereof may be used. Asthe metal constituting the metal salt, for example, zinc, magnesium,calcium, aluminum and sodium may be used, and among them, zinc ispreferred because it provides high resilience.

The amount of the co-crosslinking agent to be used is preferably 10parts or more, more preferably 20 parts or more, and is preferably 50parts or less, more preferably 40 parts or less, based on 100 parts ofthe base rubber by mass. If the amount of the co-crosslinking agent tobe used is less than 10 parts by mass, the amount of the organicperoxide must be increased to obtain an appropriate hardness, whichtends to lower the resilience. On the other hand, if the amount of theco-crosslinking agent to be used is more than 50 parts by mass, the corebecomes too hard, so that the shot feeling may be lowered.

The filler contained in the core rubber composition is mainly blended asa specific gravity adjusting agent in order to adjust the specificgravity of the golf ball obtained as the final product in the range of1.0 to 1.5, and may be blended as required. Examples of the fillerinclude an inorganic filler such as zinc oxide, barium sulfate, calciumcarbonate, magnesium oxide, tungsten powder, and molybdenum powder. Theamount of the filler to be blended in the rubber composition ispreferably 2 parts or more, more preferably 3 part or more, and ispreferably 50 parts or less, more preferably 35 parts or less based on100 parts of the base rubber by mass. If the amount of the filler to beblended is less than 2 part by mass, it becomes difficult to adjust theweight, while if it is more than 50 parts by mass, the weight ratio ofthe rubber component becomes small and the resilience tends to belowered.

As the core rubber composition, an organic sulfur compound, anantioxidant or a peptizing agent may be blended appropriately inaddition to the base rubber, the crosslinking initiator, theco-crosslinking agent and the filler.

As the organic sulfur compound, diphenyl disulfide or a derivativethereof may be preferably used. Examples of the diphenyl disulfide orthe derivative thereof include diphenyl disulfide; mono-substituteddiphenyl disulfide such as bis(4-chlorophenyl)disulfide,bis(3-chlorophenyl)disulfide, bis(4-bromophenyl)disulfide,bis(3-bromophenyl)disulfide, bis(4-fluorophenyl)disulfide,bis(4-iodophenyl)disulfide and bis(4-cyanophenyl)disulfide;di-substituted diphenyl disulfide such asbis(2,5-dichlorophenyl)disulfide, bis(3,5-dichlorophenyl)disulfide,bis(2,6-dichlorophenyl)disulfide, bis(2,5-dibromophenyl)disulfide,bis(3,5-dibromophenyl)disulfide, bis(2-chloro-5-bromophenyl)disulfide,and bis(2-cyano-5-bromophenyl)disulfide; tri-substituted diphenyldisulfide such as bis (2,4,6-trichlorophenyl)disulfide, andbis(2-cyano-4-chloro-6-bromophenyl)disulfide; tetra-substituted diphenyldisulfide such as bis(2,3,5,6-tetra chlorophenyl)disulfide;penta-substituted diphenyl disulfide such asbis(2,3,4,5,6-pentachlorophenyl)disulfide andbis(2,3,4,5,6-pentabromophenyl)disulfide. These diphenyl disulfides orthe derivative thereof can enhance resilience by having some influenceon the state of vulcanization of vulcanized rubber. Among them, diphenyldisulfide or bis(pentabromophenyl)disulfide is preferably used since thegolf ball having particularly high resilience can be obtained. Theamount of the diphenyl disulfide or the derivative thereof to be blendedis preferably 0.1 part by mass or more, more preferably 0.3 part by massor more, and is preferably 5.0 parts by mass or less, more preferably3.0 parts by mass or less relative to 100 parts by mass of the baserubber.

The amount of the antioxidant to be blended is preferably 0.1 part ormore and is preferably 1 part or less based on 100 parts of the baserubber by mass. Further, the amount of the peptizing agent is preferably0.1 part or more and is preferably 5 parts or less based on 100 parts ofthe base rubber by mass.

The conditions for press-molding the core rubber composition should bedetermined depending on the rubber composition. Specifically, thepress-molding is preferably carried out for 10 to 60 minutes at thetemperature of 130° C. to 200° C. Alternatively, the press-molding ispreferably carried out in a two-step heating, for example, for 20 to 40minutes at the temperature of 130° C. to 150° C., and continuously for 5to 15 minutes at the temperature of 160° C. to 180° C.

In the case that the core consists of a center and at least oneintermediate layer covering the center, the center can be formed fromthe core rubber composition described above. The diameter of the centeris preferably 34.8 mm or more, more preferably 35.0 mm or more, and ispreferably 41.2 mm or less, more preferably 41.0 mm or less. If thediameter of the center is less than 34.8 mm, the intermediate layer orthe cover layer must be made thicker than the desired thickness,resulting in the lowered resilience. On the other hand, if the diameterof the center is more than 41.2 mm, the intermediate layer or the covermust be made thinner than the desired thickness, and hence theintermediate layer or the cover does not function well.

In the case that the center has a diameter of from 34.8 mm to 41.2 mm,the compression deformation amount (deformation amount along theshrinkage direction) of the center when applying a load from 98 N as aninitial load to 1275 N as a final load is preferably 1.90 mm or more,more preferably 2.00 mm or more, even more preferably 2.10 mm or more,and is preferably 5.00 mm or less, more preferably 4.90 mm or less, andeven more preferably 4.80 mm or less. If the above deformation amount is1.90 mm or more, the shot feeling becomes better, while if the abovedeformation amount is 5.00 mm or less, the resilience becomes better.

The center preferably has a surface hardness of 45 or more, morepreferably 50 or more, even more preferably 55 or more, and preferablyhas a surface hardness of 65 or less, more preferably 62 or less, evenmore preferably 60 or less in Shore D hardness. If the surface hardnessof the center is 45 or more in Shore D hardness, the center is notexcessively soft, and the resilience becomes better. On the other hand,if the surface hardness of the center is 65 or less in Shore D hardness,the center does not become excessively hard and the shot feeling becomesbetter.

Examples of the material for the intermediate layer are a cured productof the rubber composition; a conventional ionomer resin; a thermoplasticpolyamide elastomer having a commercial name of “Pebax (registeredtrademark) (e.g. Pebax 2533)” available from Arkema; a thermoplasticpolyester elastomer having a commercial name of “Hytrel (registeredtrademark) (e.g. Hytrel 3548, Hytrel 4047)” available from Du Pont-TorayCo., Ltd.; a thermoplastic polyurethane elastomer having a commercialname of “Elastollan (registered trademark) (e.g. Elastollan XNY97A)”available from BASF Japan Co., a thermoplastic polystyrene elastomerhaving a commercial name of “Rabalon (registered trademark) (e.g.Rabalon SR04, Rabalon T3339C, Rabalon T3221C)” available from MitsubishiChemical Corporation. The above materials for the intermediate layer canbe used solely or as a mixture of at least two of them.

Examples of the ionomer resin include one prepared by neutralizing atleast a part of carboxyl groups in a copolymer, composed of ethylene andan α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms with ametal ion; one prepared by neutralizing at least a part of carboxylgroups in a terpolymer composed of ethylene, an α,β-unsaturatedcarboxylic acid having 3 to 8 carbons atoms, and an α,β-unsaturatedcarboxylic acid ester with a metal ion; or a mixture of these two.

Specific examples of the ionomer resins include trade name “Himilan(registered trademark) (e.g. the binary copolymerized ionomer such asHimilan 1555 (Na), Himilan 1557 (Zn), Himilan 1605 (Na), Himilan 1706(Zn), Himilan 1707 (Na), Himilan AM7311 (Mg), Himilan AM7329 (Zn); andthe ternary copolymerized ionomer such as Himilan 1856 (Na), Himilan1855 (Zn))” commercially available from Du Pont-Mitsui PolychemicalsCo., Ltd.

Further, examples include “Surlyn (registered trademark) (e.g. thebinary copolymerized ionomer such as Surlyn 8945 (Na), Surlyn 9945 (Zn),Surlyn 8140 (Na), Surlyn 8150 (Na), Surlyn 9120 (Zn), Surlyn 9150 (Zn),Surlyn 6910 (Mg), Surlyn 6120 (Mg), Surlyn 7930 (Li), Surlyn 7940 (Li),Surlyn AD8546 (Li); and the ternary copolymerized ionomer such as Surlyn6320 (Mg), Surlyn 8120 (Na), Surlyn 8320 (Na), Surlyn 9320 (Zn))” andthe ternary copolymerized ionomer such as “HPF 1000 (Mg), HPF 2000 (Mg)”commercially available from E.I. du Pont de Nemours and Company.

Further, examples include “Iotek (registered trademark) (e.g. the binarycopolymerized ionomer such as Iotek 8000 (Na), Iotek 8030 (Na), Iotek7010 (Zn), Iotek 7030 (Zn); and the ternary copolymerized ionomer suchas Iotek 7510 (Zn), Iotek 7520 (Zn))” commercially available fromExxonMobil Chemical Corporation.

It is noted that Na, Zn, Li, and Mg described in the parentheses afterthe trade names indicate metal types of neutralizing metal ions for theionomer resins. The intermediate layer may further contain a specificgravity adjusting agent such as barium sulfate or tungsten or the like;an antioxidant; or a pigment component.

A method for molding the intermediate layer is not particularly limited,and includes an embodiment which comprises injection molding theintermediate layer composition directly onto the center, or anembodiment which comprises molding the intermediate layer compositioninto a half hollow-shell, covering the center with the two hollow-shellsand subjecting the center with the two hollow-shells to thecompression-molding.

In the case of using the intermediate layer composition containing arubber composition as a main component (50 mass % or more), theintermediate layer preferably has a thickness of 1.2 mm or more, morepreferably 1.8 mm or more, even more preferably 2.4 mm or more, andpreferably has a thickness of 6.0 mm or less, more preferably 5.2 mm orless, even more preferably 4.4 mm or less.

In the case of using the intermediate layer composition containing theresin composition as a main component (50 mass % or more), theintermediate layer preferably has a thickness of 0.3 mm or more, morepreferably 0.4 mm or more, even more preferably 0.5 mm or more, andpreferably has a thickness of 2.5 mm or less, more preferably 2.4 mm orless, even more preferably 2.3 mm or less. If the thickness of theintermediate layer is more than 2.5 mm, the resilience performance ofthe obtained golf ball may be lowered, while if the thickness of theintermediate layer is less than 0.3 mm, it may be difficult to suppressthe excessive spin rate on the driver shot.

The intermediate layer of the golf ball of the present inventionpreferably has a slab hardness of 30 or larger, more preferably 34 orlarger, and even more preferably 37 or larger, and preferably has a slabhardness of 65 or smaller, more preferably 62 or smaller, and even morepreferably 60 or smaller in Shore D hardness. The intermediate layerhaving the slab hardness of 30 or more in shore D hardness makes thecore have the higher degree of “hard outer and soft inner” structure,thereby providing a high launch angle and a less amount of spin andhence achieving a great flight distance of the gold ball. On the otherhand, the intermediate layer having the slab hardness of 65 or less inshore D hardness provides an excellent shot feeling as well as improvesthe spin performance of the golf ball, thereby improving controllabilityof the golf ball. Herein, the slab hardness of the intermediate layer isthe measured hardness of the intermediate layer composition in the formof a sheet, and is measured by a later-described measuring method. Theslab hardness of the intermediate layer can be adjusted, for example, byappropriately selecting a combination of the above resin component andthe rubber material and the amount of additives.

The core used in the golf ball of the present invention preferably has adiameter of 40.4 mm or larger, more preferably 40.6 mm or larger, andeven more preferably 40.8 mm or larger, and preferably has a diameter of42.4 mm or smaller, more preferably 42.3 mm or smaller, and even morepreferably 42.2 mm or smaller. If the diameter of the core is smallerthan the above lower limit, the cover becomes so thick that theresulting golf ball would have reduced resilience. On the other hand, ifthe diameter of the core is larger than the above upper limit, the coverbecomes so thin that it is difficult to mold a cover.

In the case that the core has a diameter of from 40.4 mm to 42.4 mm, thecompression deformation amount (deformation amount along the shrinkagedirection) of the core when applying a load from 98 N as an initial loadto 1275 N as a final load is preferably 1.9 mm or more, more preferably2.0 mm or more, even more preferably 2.1 mm or more, and is preferably4.7 mm or less, and more preferably 4.5 mm or less. If the abovedeformation amount is less than 1.9 mm, the shot feeling becomes poor,while if the above deformation amount is larger than 4.7 mm, theresilience may be lowered.

The center hardness of the core is preferably 30 or larger, morepreferably 32 or larger, and even more preferably 35 or larger in ShoreD hardness. If the center hardness is smaller than 30 in Shore Dhardness, the core becomes so soft that the resilience of the golf balltends to become lower. The center hardness of the core is preferably 50or smaller, more preferably 48 or smaller, and even more preferably 45or smaller in Shore D hardness. If the center hardness is more than 50in Shore D hardness, the core becomes too hard, resulting in the poorshot feeling. In the present invention, the center hardness of the coreis the hardness measured with the Shore D type spring hardness tester atthe central point of a cut plane of a core which has been cut into twohalves.

The surface hardness of the core is preferably 20 or larger, morepreferably 25 or larger, and even more preferably 30 or larger in ShoreD hardness. If the surface hardness is less than 20 in Shore D hardness,the core becomes so soft and the resilience may be lowered. The surfacehardness of the core is preferably 70 or smaller, more preferably 69 orsmaller, and even more preferably 68 or smaller in shore D hardness. Ifthe surface hardness is more than 70 in Shore D hardness, the corebecomes so hard and the shot feeling may be lowered.

In one preferable embodiment, the core having the surface hardnesslarger than the center hardness may be used as the core. The hardnessdifference (surface hardness−center hardness) between the surfacehardness and the center hardness of the core in the golf ball of thepresent invention is preferably 4 or larger, more preferably 7 or largerin Shore D hardness. If the surface hardness is larger than the centerhardness, the launch angle becomes high and the spin rate becomes low,thereby improving the flight distance. Further, in this case, thehardness difference (surface hardness−center hardness) between thesurface hardness and the center hardness of the core in the golf ball ofthe present invention is preferably 40 or less, more preferably 35 orless. If the hardness difference is too large, the durability of thegolf ball may deteriorate.

When preparing a wound golf ball in the present invention, a wound coremay be used as the core. In that case, for example, a wound corecomprising a center formed by curing the above rubber composition forthe core and a rubber thread layer which is formed by winding a rubberthread around the center in an elongated state can be used. In thepresent invention, the rubber thread, which is conventionally used forwinding around the center, can be adopted for winding around the center.The rubber thread, for example, is obtained by vulcanizing a rubbercomposition including a natural rubber, or a mixture of a natural rubberand a synthetic polyisoprene, a sulfur, a vulcanization auxiliary agent,a vulcanization accelerator, and an antioxidant. The rubber thread iswound around the center in elongation of about 10 times length to formthe wound core.

EXAMPLES

Hereinafter, the present invention will be described in detail by way ofexample. The present invention is not limited to examples describedbelow. Various changes and modifications can be made without departingfrom the spirit and scope of the present invention.

[Evaluation Method]

(1) Hardness of Center and Core (Shore D Hardness)

A type P1 auto loading durometer manufactured by Kobunshi Keiki Co.,Ltd., provided with a Shore D type spring hardness tester prescribed inASTM-D2240 was used to measure the surface hardness and the centerhardness of the center and the core. Shore D hardness measured at thesurfaces of the center and the core are defined as the surface hardnessof the center and the core, respectively. The core was cut into twohemispheres to obtain a cut plane, and a Shore D hardness measured atthe center of the cut plane was used as the center hardness of the core.

(2) Slab Hardness (Shore D Hardness)

Sheets with a thickness of about 2 mm were produced by heat-pressing thecover composition and the intermediate layer composition, and stored at23° C. for two weeks. Three or more of these sheets were stacked on oneanother so as not to be affected by the measuring substrate on which thesheets were placed, and the hardness of the stack was measured with atype P1 auto loading durometer manufactured by Kobunshi Keiki Co., Ltd.,provided with a Shore D type spring hardness tester prescribed inASTM-D2240.

(3) Compression Deformation Amount (mm)

A compression deformation amount of the center, core and golf ball (ashrinking amount of the center, core, and golf ball in the compressiondirection thereof), when applying a load from 98 N as an initial load to1275 N as a final load to the center, core and golf ball, was measured.

(4) Melt Flow Rate (MFR) (g/10 min)

The MFR was measured using a flow tester (Shimadzu flow tester CFT-100Cmanufactured by Shimadzu Corporation) in accordance with JIS K7210. Themeasurement was conducted under the conditions of the measurementtemperature 190° C. and the load of 2.16 kg.

(5) Adhesion of Paint Film

Each painted golf ball was hit 100 times repeatedly with a driver (1W)attached to a swing robot manufactured by TRUETEMPER CO, at the headspeed of 45 m/sec. The degree of the peeling of the paint film wasobserved and evaluated based on the following criteria.

G (Good): The paint film did not peel off at all, or the area where thepaint film peeled off was less than 1 mm².

P (Poor): The area where the paint film peeled off was 1 mm² or more.

(6) Flight Distance

A metal-head W#1 driver (XXIO, S shaft, loft: 10.0°, manufactured by SR1Sports Limited) was installed on a swing robot manufactured byTRUETEMPER CO. Golf balls were hit at a head speed of 45 m/sec, and theflight distances (the distance from the launch point to the stop point)were measured. This measurement was conducted ten times for each golfball, and the average value was used as the flight distance of the golfball.

(7) Durability

A metal-head W#1 driver (XXIO, S shaft, loft: 11°, manufactured by SR1Sports Limited) was installed on a swing robot manufactured by GolfLaboratories, Inc. Each golf ball was hit at a head speed of 45 m/sec.This procedure was repeated, and the number of hits required to breakthe golf ball was counted. The number of hits for golf ball No. 11 wasdefined as an index of 100, and the durability of each golf ball wasrepresented by converting the number of hits for each golf ball intothis index. A greater index value indicates that the durability of thegolf ball is excellent.

(8) FT-IR Measurement

Measuring samples were taken from the pellet of the cover compositionbefore injection molding and the cover after molding. These samples wereanalyzed with Fourier transform infrared spectrophotometer (Auto IMAGEFT-IR) available from PerkinElmer, Inc by a macro ATR method (germaniumprism, observation diameter: about 1 mm). The area A under a peak around1600 cm⁻¹ and the area B under a peak around 1700 cm⁻¹ were determinedfrom the obtained spectrum. FIG. 1 shows a FT-IR spectrum of the coverof the golf ball No. 1 (vertical axis: absorbance). Base lines weredrawn for Peak A around 1600 cm⁻¹ and Peak B around 1700 cm⁻¹,respectively, as shown FIG. 1 and area A, B were calculated. It is notedthat Peak A around 1600 cm⁻¹ may shift depending on kinds of metalneutralizing the carboxyl group.

[Production of Golf Balls]

(1) Production of Center

The center rubber compositions having the formulations shown in Table 1were kneaded and heat-pressed in upper and lower molds, each having ahemispherical cavity, at 170° C. for 20 minutes to prepare sphericalcenters. The amount of barium sulfate was adjusted appropriately to makea golf ball have a weight of 45.4 g.

TABLE 1 Center Rubber Composition Parts by mass FormulationPolybutadiene 100 Zinc acrylate 27 Zinc oxide 5 Dicumyl peroxide 0.9Diphenyl disulfide 0.5 Barium sulfate Appropriate amount*) PropertiesDiameter (mm) 39.2 Compression deformation amount 3.8 (mm) Centerhardness (Shore D) 41 Surface hardness (Shore D) 50 Formulation: partsby mass *)Depending on the cover composition, adjustment was made suchthat the golf ball had a mass of 45.4 g. Polybutadiene rubber: “BR-730(high-cis polybutadiene)” manufactured by JSR Corporation. Zincacrylate: “ZNDA-90S” manufactured by Nihon Jyoryu Kogyo Co., Ltd. Zincoxide: “Ginrei R” manufactured by Toho Zinc Co., Ltd. Barium sulfate:“Barium Sulfate BD” manufactured by Sakai Chemical Industry Co., Ltd.Diphenyl disulfide: manufactured by Sumitomo Seika Chemicals Co., Ltd.Dicumyl peroxide: “Percumyl (registered trademark) D” manufactured byNOF Corporation.(2) Preparation of Intermediate Layer Composition and Cover Composition

Blending materials shown in Tables 2 to 6 were mixed with a twin-screwkneading extruder to prepare the intermediate layer composition andcover compositions in the pellet form. The extruding conditions of thecover composition were a screw diameter of 45 mm, a screw rotationalspeed of 200 rpm, and screw L/D=35, and the cylinder temperature of 140to 200° C. The extruding conditions of the intermediate layercomposition were a screw diameter of 45 mm, a screw rotational speed of200 rpm, and screw L/D=35, and the mixtures were heated to 160 to 230°C. at the die position of the extruder.

TABLE 2 Intermediate layer composition Parts by mass Surlyn 8945 35Himilan AM7329 30 Rabalon T3221C 35 Titanium oxide 4 Melt flow rate(190° C., 2.16 kg) (g/10 min) 5 Slab hardness (Shore D) 48 Note on Table2: SURLYN 8945: a sodium ion neutralized ethylene-methacrylic acidcopolymer ionomer resin available from E.I. du Pont de Nemours andCompany. Himilan AM7329: Zinc ion neutralized ethylene-methacrylic acidcopolymer ionomer resin available from Du Pont-Mitsui Polychemicals Co.,Ltd Rabalon T3221C: Polystyrene elastomer available from MitsubishiChemical Corporation.(3) Production of Golf Ball Body

The intermediate layer compositions obtained above were injection-moldedonto the spherical centers to form the intermediate layers (thickness:1.0 mm) covering the centers. Subsequently, golf balls were produced byinjection-molding the cover composition on the intermediate layer toform the cover. Upper and lower molds have a spherical cavity withpimples, a part of which serves as a hold pin which is extendable andretractable. The cover composition was heated to 200 to 260° C. at thecylinder portion of the injection unit and injected into the moldclamped under a pressure of 15 MPa, and then cooled for 30 seconds. Themold was opened, and the golf ball bodies were taken out from the mold.The surface of the obtained golf ball bodies were treated withsandblast, marked, and painted with a clear paint. The paint was driedin an oven at 40° C. to form a paint film having a thickness of 10 μm,and golf balls having a diameter of 42.8 mm and a mass of 45.4 g wereobtained. As the clear paint, a following paint was used.

[Preparation of Clear Paint]

(i) Base Material: Urethane Polyol

60 parts by mass of PTMG250 (BASF Co., polyoxytetramethyleneglycolhaving a molecular weight of 250), 54 parts by mass of 550U(Sumitomo-Bayer Urethane Co., Ltd, branched polyol having a molecularweight of 550) were dissolved into 120 parts by mass of the solvent(toluene and methylethylketone). The dibutyl-tin-dilaurylate was addedin an amount of 0.1 mass % with respect to the total base material.While keeping this polyol at the temperature of 80° C., 66 parts by massof isophorone diisocyanate was slow-added into the polyol to obtain aurethane polyol having a solid content of 60 mass %, hydroxyl value of75 mg KOH/g, and a weight average molecular weight of 7808.

(ii) Curing agent: Isophorone diisocyanate available from Sumitomo-BayerUrethane Co., LTD.

(iii) Mixing ratio: NCO (curing agent)/OH (base material)=1.2 molarratio.

TABLE 3 Golf ball No. 1 2 3 4 5 Cover Resin (A) Component Himilan AM7329(Zn) 70 70 — — 60 Composition component Surlyn 9150 (Zn) — — 70 — —Surlyn 9120 (Zn) — — — 60 — Surlyn 8945 (Na) — — — — — Himilan 1557 (Zn)— — — — — (B) component Nucrel N1050H 30 — — 40 40 Nucrel N2050H — 30 30— — PRIMACOR 5980I — — — — — Nucrel N1560 — — — — — (C) component Zincoxide 2 5 5 1 13 Zinc hydroxide — — — — — Zinc carbonate — — — — —Magnesium stearate — — — — — Titanium oxide 3 3 3 3 3 Ultra marine blue0.04 0.04 0.04 0.04 0.04 P1 = A1/(A1 + B1) 0.40 0.38 0.32 0.27 0.40 P2 =P2/(P1 + B2) 0.82 0.90 0.76 0.58 1.00 P2/P1 2.1 2.4 2.4 2.1 2.5Properties Melt flow rate (g/10 min) 22 19 16 16 15 Slab hardness (ShoreD) 60 63 65 60 61 Bending stiffness (MPa) 195 221 255 304 272 Core Corecenter hardness (Shore D) 41 41 41 41 41 Properties Core surfacehardness (Shore D) 51 51 51 51 51 Compression deformation amount (mm)3.50 3.50 3.50 3.50 3.50 Golf ball Cover thickness (mm) 0.8 0.8 0.8 0.80.8 Properties Compression deformation amount (mm) 3.20 3.18 3.17 3.203.18 Adhesion of Paint Film G G G G G Flight distance (m) 233 235 236236 236 Durability (Index) 120 112 109 114 115 Formulation: parts bymass

TABLE 4 Golf ball No. 6 7 8 9 10 Cover Resin (A) Component HimilanAM7329 (Zn) — — 80 — — Composition component Surlyn 9150 (Zn) 70 70 — —— Surlyn 9120 (Zn) — — — 50 — Surlyn 8945 (Na) — — — — — Himilan 1557(Zn) — — — — 70 (B) component Nucrel N1050H — 30 — 50 30 Nucrel N2050H —— 20 — — PRIMACOR 5980I 30 — — — — Nucrel N1560 — — — — — (C) componentZinc oxide 2 — 0.1 — 4 Zinc hydroxide — 0.2 — — — Zinc carbonate — — —15 — Magnesium stearate — — — — — Titanium oxide 3 3 3 3 3 Ultra marineblue 0.04 0.04 0.04 0.04 0.04 P1 = A1/(A1 + B1) 0.27 0.25 0.39 0.42 0.38P2 = P2/(P1 + B2) 0.57 0.38 0.64 0.94 0.81 P2/P1 2.1 1.6 1.6 2.2 2.1Properties Melt flow rate (g/10 min) 18 21 15 16 19 Slab hardness (ShoreD) 62 62 62 61 59 Bending stiffness (MPa) 230 214 194 340 207 Core Corecenter hardness (Shore D) 41 41 41 41 41 Properties Core surfacehardness (Shore D) 51 51 51 51 51 Compression deformation amount (mm)3.50 3.50 3.50 3.50 3.50 Golf ball Cover thickness (mm) 0.8 0.8 0.8 0.80.8 Properties Compression deformation amount (mm) 3.18 3.19 3.19 3.173.21 Adhesion of Paint Film G G G G G Flight distance (m) 235 234 233237 233 Durability (Index) 107 106 118 103 100 Formulation: parts bymass

TABLE 5 Golf ball No. 11 12 13 14 15 Cover Resin (A) Component HimilanAM7329 (Zn) 70 70 70 60 — Composition component Surlyn 9150 (Zn) — — — —— Surlyn 9120 (Zn) — — — — — Surlyn 8945 (Na) — — — 10 — Himilan 1557(Zn) — — — — 70 (B) component Nucrel N1050H 30 30 30 30 30 Nucrel N2050H— — — — — PRIMACOR 5980I — — — — — Nucrel N1560 — — — — — (C) componentZinc oxide — — — 1 — Zinc hydroxide — — 21 — — Zinc carbonate — — — — —Magnesium stearate — 10 — — — Titanium oxide 3 3 3 3 3 Ultra marine blue0.04 0.04 0.04 0.04 0.04 P1 = A1/(A1 + B1) 0.39 0.48 0.39 0.40 0.38 P2 =P2/(P1 + B2) 0.39 0.50 1.00 0.81 0.38 P2/P1 1.0 1.0 2.6 2.0 1.0Properties Melt flow rate (g/10 min) 25 31 *1) 23 25 Slab hardness(Shore D) 59 57 — 60 57 Bending stiffness (MPa) 178 170 — 192 174 CoreCore center hardness (Shore D) 41 41 — 41 41 Properties Core surfacehardness (Shore D) 51 51 — 51 51 Compression deformation amount (mm)3.50 3.50 — 3.50 3.50 Golf ball Cover thickness (mm) 0.8 0.8 — 0.8 0.8Properties Compression deformation amount (mm) 3.20 3.21 — 3.19 3.22Adhesion of Paint Film G P — G G Flight distance (m) 232 231 — 233 231Durability (Index) 100 70 — 98 57 Formulation: parts by mass *1)Impossible to mold

TABLE 6 Golf ball No. 16 17 18 Cover Resin (A) Component Himilan AM7329(Zn) 70 90 40 Composition component Surlyn 9150 (Zn) — — — Surlyn 9120(Zn) — — — Surlyn 8945 (Na) — — — Himilan 1557 (Zn) — — — (B) componentNucrel N1050H — 10 60 Nucrel N2050H — — — PRIMACOR 5980I — — — NucrelN1560 30 — — (C) component Zinc oxide — 5 5 Zinc hydroxide — — — Zinccarbonate — — — Magnesium stearate — — — Titanium oxide 3 3 3 Ultramarine blue 0.04 0.04 0.04 P1 = A1/(A1 + B1) 0.35 0.48 0.35 P2 =P2/(P1 + B2) 0.35 1.00 0.82 P2/P1 1.0 2.1 2.4 Properties Melt flow rate(g/10 min) 13 *1) 70 Slab hardness (Shore D) 61 — 55 Bending stiffness(MPa) 257 — 177 Core Core center hardness (Shore D) 41 — 41 PropertiesCore surface hardness (Shore D) 51 — 51 Compression deformation amount(mm) 3.50 — 3.50 Golf ball Cover thickness (mm) 0.8 — 0.8 PropertiesCompression deformation amount (mm) 3.20 — 3.23 Adhesion of Paint Film G— G Flight distance (m) 234 — 225 Durability (Index) 75 — 10Formulation: parts by mass *1) Impossible to moldNotes on Tables No. 3 to No. 6HIMILAN AM7329: a zinc ion neutralized ethylene-methacrylic acidcopolymer ionomer resin (Acid content: 15 mass % or more, Bendingstiffness: 221 MPa, Melt Flow Rate (190° C., 2.16 kg): 5 g/10 min)available from Du Pont-Mitsui Polychemicals Co., Ltd.SURLYN 9150: a zinc ion neutralized ethylene-methacrylic acid copolymerionomer resin (Acid content: 15 mass % or more, Bending stiffness: 270MPa, Melt Flow Rate (190° C., 2.16 kg): 4.5 g/10 min) available fromE.I. du Pont de Nemours and Company.SURLYN 9120: a zinc ion neutralized ethylene-methacrylic acid copolymerionomer resin (Acid content: 15 mass % or more, Bending stiffness: 440MPa, Melt Flow Rate (190° C., 2.16 kg): 1.3 g/10 min) available fromE.I. du Pont de Nemours and Company.SURLYN 8945: a sodium ion neutralized ethylene-methacrylic acidcopolymer ionomer resin (Acid content: 15 mass % or more, Bendingstiffness: 272 MPa, Melt Flow Rate (190° C., 2.16 kg): 4.5 g/10 min)available from E.I. du Pont de Nemours and Company.HIMILAN 1557: a zinc ion neutralized ethylene-methacrylic acid copolymerionomer resin (Acid content: less than 15 mass %, Bending stiffness: 215MPa, Melt Flow Rate (190° C., 2.16 kg): 5.5 g/10 min, Shore D hardness:59) available from Du Pont-Mitsui Polychemicals Co., Ltd.Nucrel 1050H: an ethylene-methacrylic acid copolymer (melt flow rate(190° C.*2.16 kg): 500 g/10 min, Bending stiffness: 79 MPa) availablefrom Du Pont-Mitsui Polychemicals Co., Ltd.Nucrel 2050H: an ethylene-methacrylic acid copolymer (melt flow rate(190° C.*2.16 kg): 500 g/10 min, Bending stiffness: 82 MPa) availablefrom Du Pont-Mitsui Polychemicals Co., Ltd.Nucrel N1560: an ethylene-methacrylic acid copolymer (melt flow rate(190° C.*2.16 kg): 60 g/10 min, Shore D hardness: 53, Bending stiffness:83 MPa) available from Du Pont-Mitsui Polychemicals Co., Ltd.PRIMACOR 59801: an ethylene-acrylic acid copolymer (melt flow rate (190°C.*2.16 kg): 300 g/10 min, Bending stiffness: 80 MPa) available from DowChemical Company.Zinc oxide: Yoneyama Yakuhin Kogyo Co., LTD (no surface treatment)Zinc hydroxide: Yoneyama Yakuhin Kogyo CO., LTDZinc carbonate: Yoneyama Yakuhin Kogyo CO., LTD

The golf ball resin compositions comprising, (A) an ionomer resinconsisting of a metal ion-neutralized product of a binary copolymercomposed of an olefin and an α,β-unsaturated carboxylic acid having 3 to8 carbon atoms; (B) a binary copolymer composed of an olefin and anα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and (C) azinc compound, wherein a content ratio ((A)/(B)) of (A) component to (B)component ranges from 50/50 to 80/20 in a mass ratio and a content of(C) component ranges from 0.1 part to 20 parts with respect to 100 partsby mass of a sum of (A) component and (B) component, and the golf ballresin component has a melt flow rate (190° C., 2.16 kg) of 15 g/10 minor more were excellent in fluidity, and enabled to mold a thin cover.Further, P2/P1 were 1.5 or more in every golf ball resin composition ofthe present invention, thus it is confirmed that the neutralization wasconducted with (C) the zinc compound. Golf balls No. 1 to No. 10, andNo. 14 using these golf ball resin compositions were excellent in thedurability and flight distance, irrespective of having a cover with ahigh hardness.

Golf ball No. 12 is the case that the metal salt of a fatty acid wasused to improve the fluidity. Since the metal salt of the fatty acidbleed out from the surface of the golf ball body, the adhesion of thepaint film was lowered. Because of too low fluidity, it was impossibleto mold Golf ball No. 13. Golf ball No. 15 is the case that (C) the zinccompound was not contained. The durability was lowered. In Golf ball No.16, since the melt flow rate was as low as 13 g/10 min, it was necessaryto increase the molding temperature to 300° C. Therefore, the resincomponent constituting the cover composition thermally decomposed andthe durability was lowered. Golf ball No. 17 was the case that thecontent of (A) component was too high. It was impossible to mold thegolf ball. Golf ball No. 18 was the case the content of (A) componentwas too low. The flight distance and the durability was lowered.

The present invention is suitable for the golf ball having an ionomercover. This application is based on Japanese Patent application No.2010-102533 filed on Apr. 27, 2010, the contents of which are herebyincorporated by reference.

The invention claimed is:
 1. A golf ball resin composition comprising, aresin component and (C) a zinc compound, wherein the resin componentconsists of (A) an ionomer resin consisting of a metal ion-neutralizedproduct of a binary copolymer composed of an olefin and anα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and (B) abinary copolymer composed of an olefin and an α,β-unsaturated carboxylicacid having 3 to 8 carbon atoms, wherein a content ratio ((A)/(B)) of(A) component to (B) component ranges from 50/50 to 80/20 in a massratio and a content of (C) component ranges from 0.1 part to 20 partswith respect to 100 parts by mass of a sum of (A) component and (B)component, and the golf ball resin composition has a melt flow rate(190° C., 2.16 kg) of 15 g/10 min or more and a slab hardness rangingfrom 61 to 70 in Shore D hardness, wherein (A) the ionomer resin has amelt flow rate (190° C., 2.16 kg) ranging from 0.1 g/10 min to 30 g/10min, and wherein (B) the binary copolymer has a melt flow rate (190° C.,2.16 kg) ranging from 100 g/10 min to 1000 g/10 min.
 2. The golf ballresin composition according to claim 1, wherein (A) the ionomer resinhas the α,β-unsaturated carboxylic acid component in a content of 15mass % or more.
 3. The golf ball resin composition according to claim 1,wherein (A) the ionomer resin is neutralized with zinc.
 4. The golf ballresin composition according to claim 1, wherein (C) the zinc compound iszinc oxide, zinc hydroxide, or zinc carbonate.
 5. The golf ball resincomposition according to claim 1, wherein A1, A2, B1, and B2 definedbelow satisfy following expressions:P1=A1/(A1+B1)P2=A2/(A2+B2)0.2≦P1≦1.00.3≦P2≦1.01.5≦P2/P1≦2.5 wherein A1 is defined as an area under a peak around 1600cm⁻¹ and B1 is defined as an area under a peak around 1700 cm⁻¹ in aspectrum obtained by analyzing the golf ball composition beforeinjection molding by FT-IR, and A2 is defined as an area under a peakaround 1600 cm⁻¹ and B2 is defined as an area under a peak around 1700cm⁻¹ in a spectrum obtained by analyzing the golf ball composition afterinjection molding by FT-IR.
 6. The golf ball resin composition accordingto claim 1, wherein a degree of neutralization of the carboxyl groupscontained in (A) the ionomer resin ranges from 15 mole % to 90 mole %.7. The golf ball resin composition according to claim 1, wherein (A) theionomer resin has a bending stiffness ranging from 140 MPa to 550 MPa.8. The golf ball resin composition according to claim 1, wherein (A) theionomer resin has a slab hardness ranging from 50 to 75 in Shore Dhardness.
 9. A golf ball comprising a constituent member formed byinjection molding a golf ball resin composition which comprises a resincomponent and (C) a zinc compound, wherein the resin component consistsof (A) an ionomer resin consisting of a metal ion-neutralized product ofa binary copolymer composed of an olefin and an α,β-unsaturatedcarboxylic acid having 3 to 8 carbon atoms and (B) a binary copolymercomposed of an olefin and an α,β-unsaturated carboxylic acid having 3 to8 carbon atoms, wherein a content ratio ((A)/(B)) of (A) component to(B) component ranges from 50/50 to 80/20 in a mass ratio and a contentof (C) component ranges from 0.1 part to 20 parts with respect to 100parts by mass of a sum of (A) component and (B) component, and the golfball resin composition has a melt flow rate (190° C., 2.16 kg) of 15g/10 min or more and a slab hardness ranging from 61 to 70 in Shore Dhardness, wherein (A) the ionomer resin has a melt flow rate (190° C.,2.16 kg) ranging from 0.1 g/10 min to 30 g/10 min, and wherein (B) thebinary copolymer has a melt flow rate (190° C., 2.16 kg) ranging from100 g/10 min to 1000 g/10 min.
 10. The golf ball according to claim 9,wherein the constituent member is a cover.
 11. The golf ball accordingto claim 10, wherein the cover has a thickness ranging from 0.5 mm to1.5 mm.
 12. The golf ball according to claim 10, wherein the golf ballhas an intermediate layer with a thickness ranging from 0.3 mm to 6.0mm.
 13. The golf ball according to claim 12, wherein the intermediatelayer has a hardness ranging from 30 to 65 in Shore D hardness.
 14. Thegolf ball according to claim 9, wherein (A) the ionomer resin has theα,β-unsaturated carboxylic acid component in a content of 15 mass % ormore, and is neutralized with zinc.
 15. The golf ball according to claim9, wherein (A) the binary ionomer resin has a bending stiffness rangingfrom 140 MPa to 550 MPa, a melt flow rate (190° C., 2.16 kg) rangingfrom 0.1 g/10 min to 30 g/10 min, and a slab hardness ranging from 50 to75 in Shore D hardness.
 16. The golf ball according to claim 9, wherein(C) the zinc compound is zinc oxide, zinc hydroxide, or zinc carbonate.17. The golf ball according to claim 9, wherein A1, A2, B1, and B2defined below satisfy following expressions:P1=A1/(A1+B1)P2=A2/(A2+B2)0.2≦P1≦1.00.3≦P2≦1.01.5≦P2/P1≦2.5 wherein A1 is defined as an area under a peak around 1600cm⁻¹ and B1 is defined as an area under a peak around 1700 cm⁻¹ in aspectrum obtained by analyzing the golf ball composition beforeinjection molding by FT-IR, and A2 is defined as an area under a peakaround 1600 cm⁻¹ and B2 is defined as an area under a peak around 1700cm⁻¹ in a spectrum obtained by analyzing the golf ball composition afterinjection molding by FT-IR.